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Pos(FRAPWS2016)045 fields field Dissipation field of Radio Pulsars

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Pos(FRAPWS2016)045 fields field Dissipation field of Radio Pulsars SGR/AXP - are they magnetars? PoS(FRAPWS2016)045 G.S.Bisnovatyi-Kogan Space Research Institute, Profsoyuznaya∗ str. 84/32, Moscow 117997, Russia, and National Research Nuclear University "MEPHI", Kashirskoye Shosse, 31, Moscow 115409, Russia E-mail: [email protected] The observational properties of Soft Gamma Repeaters and Anomalous X-ray Pulsars (SGR/AXP) indicate to necessity of the energy source different from a rotational energy of a neu- tron star. The model, where the source of the energy is connected with a magnetic field dissipation in a highly magnetized neutron star (magnetar) is analyzed. Some observational inconsistencies are indicated for this interpretation. Slow rotating radiopulsars with very high magnetic fields were discovered, which don’t show any features of SGR, there are SGR/AXP in which an upper limit of the dipole magnetic field strength corresponds to average magnetic field of radio pulsars. The energy source, connected with the nuclear energy of superheavy nuclei stored in the nonequi- librium layer of low mass neutron star is discussed. The losses of rotational energy, observed in SGR/AXP are connected with a magnetised stellar wind, induced by the bursting events near the neutron star surface. Frontier Research in Astrophysics – II 23-28 May 2016 Mondello (Palermo), Italy ∗Speaker. ⃝c Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND 4.0). http://pos.sissa.it/ SGR/AXP - are they magnetars? G.S.Bisnovatyi-Kogan 1. Introduction Neutron stars (NS) are formed as a result of a collapse of the core of a massive star with a mass M >∼ 12M⊙. Conservation of the magnetic flux gives an estimation of NS magnetic field as 2 11 13 Bns = Bs(Rs=Rns) , Bs = 10÷100 Gs, at R ∼ (3÷10)R⊙; Rns = 10 km, Bns = 4·10 ÷5·10 Gs (Ginzburg 1964). Estimation of the NS magnetic field is obtained in radio pulsars by measurements of their rotational period and its time derivative, in the model of a dipole radiation, or pulsar wind model (Pacini 1967; Goldreich and Julian 1969) Timing observations of single radiopulsars give the fol- PoS(FRAPWS2016)045 11 13 lowing estimation Bns = 2 · 10 ÷ 5 · 10 Gs (Lorimer 2005). Figure 1: P - P˙ diagram for radiopulsars. Pulsars in binary systems with low-eccentricity orbits are encir- cled, and in high-eccentricity orbits are marked with ellipses. Stars show pulsars suspected to be connected with supernova remnants, from Lorimer (2005). 1 SGR/AXP - are they magnetars? G.S.Bisnovatyi-Kogan The pulsars with a small magnetic field in the left lower angle decrease their magnetic field during recycling by accretion in a close binary. see Bisnovatyi-Kogan (2006). SGR are single neutron stars with periods 2 ÷ 8 seconds They produce "giant bursts", when their luminosity L in the peak increase 5 ÷ 6 orders of magnitude. Having a slow rotation, and small rotational energy, their observed average luminosity exceeds rotational loss of energy more than 10 times, and orders of magnitude during the giant outbursts. It was suggested by Duncan and Thompson (1995), that the source of energy is their huge magnetic field, 2 or 3 order of a magnitude larger, then the average field in radiopulsars. Such objects were called magnetars. PoS(FRAPWS2016)045 2. SGR, giant bursts, and short GRB First two Soft Gamma Repeaters (SGR) had been discovered by KONUS group in 1979. The first one, FXP 0520 - 66, was discovered after the famous giant 5 March 1979 burst (Mazets et al. 1979b,c; Golenetskii et al. 1979), see also Mazets et.al (1982). In another source B1900+14 only small recurrent bursts had been observed (Mazets et al. 1979a). Now these sources are known under names SGR 0520 - 66 and SGR 1900+14 respectively. The third SGR 1806-20 was identified as a repetitive source by Laros et.al. (1986a,b). The first detection of this source as GRB070179 was reported by Mazets et al.(1981), and it was indicated by Mazets et al. (1982), that this source, having an unusually soft spectrum, can belong to a separate class of repetitive GRB, similar to FXP0520 - 66 and B1900+14. This suggestion was completely confirmed. The forth known SRG1627-41, showing giant burst, was discovered in 1998 almost simultaneously by BATSE (Kouveliotou et al. 1998a), and BeppoSAX (Feroci et al. 1998). The giant bursts had been observed until now in 4 sources. 2.1 SGR0526-66 It was discovered due to a giant burst of 5 March 1979, projected to the edge of the SNR N49 in LMC, and described by (Mazets et al. 1979b,c; Golenetskii et al. 1979, Mazets et.al 1982). Accepting the distance 55 kpc to LMC, the peak luminosity in the region Eg > 30 keV was 45 44 Lp ≥ 3:6 × 10 ergs/s, the total energy release in the peak Qp ≥ 1:6 × 10 ergs, in the subsequent × 44 rec tail Qt = 3:6 10 ergs. The short recurrent bursts have peak luminosities in this region Lp = 3 × 1041 − 3 × 1042 ergs/s, and energy release Qrec = 5 × 1040 − 7 × 1042 ergs. The tail was observed about 3 minutes and had regular pulsations with the period P ≈ 8 s. There was not a chance to measure P˙ in this object. 2.2 SGR1900+14 Detailed observations of this source are described by Mazets et al. (1999b,c), Kouveliotou et al. (1999), Woods et al. (1999). The giant burst was observed 27 August, 1998. The source lies close to the less than 104 year old SNR G42.8+0.6, situated at distance ∼ 10 kpc. Pulsations had been observed in the giant burst, as well as in the X-ray emission observed in this source in quiescence by RXTE and ASCA. P˙ was measured, being strongly variable. Accepting the distance 44 43 10 kpc, this source had in the region Eg > 15 keV: Lp > 3:7 × 10 ergs/s, Qp > 6:8 × 10 ergs, × 43 rec × 40 − × 41 rec × 39 − × 41 Qt = 5:2 10 ergs, Lp = 2 10 4 10 ergs/s, Q = 2 10 6 10 ergs, P = 2 SGR/AXP - are they magnetars? G.S.Bisnovatyi-Kogan 5:16 s, P˙ = 5 × 10−11 − 1:5 × 10−10 s/s. The X-ray pulsar in the error box of this source was discovered by Hurley et al. (1999b). This source was discovered also in radio band, at frequency max 111 MHz as a faint, Lr = 50 mJy, radiopulsar (Shitov 1999), with the same P and variable P˙, good corresponding to X-ray and gamma-ray observations. The values of P and average P˙ 34 correspond to the rate of a loss of rotational energy E˙rot = 3:5 × 10 ergs/s, and magnetic field 14 B = 8 × 10 Gs. The age of the pulsar estimated as tp = P=2P˙ = 700 years is much less than the estimated age of the close nearby SNR. Note that the observed X-ray luminosity of this object 35 36 Lx = 2×10 − 2×10 ergs/s is much higher, than rate of a loss of rotational energy, what means that rotation cannot be a source of energy in these objects. It was suggested that the main source PoS(FRAPWS2016)045 of energy comes from a magnetic field annihilation, and such objects had been called as magnetars by Duncan and Thompson (1992). 2.3 SGR1806-20 The giant burst from this source was observed in December 27, 2004 (Palmer et al. 2005, Mazets et al. 2005, Frederiks et al. 2007). Recurrent bursts had been studied by Kouveliotou et al. (1998b), Hurley et al. (1999a). Connection with the Galactic radio SNR G10.0-03 was found. The source has a small but significant displacement from that of the non-thermal core of this SNR. The distance to SNR is estimated as 14.5 kpc. The X-ray source observed by ASCA and RXTE in this object shows regular pulsations with a period P = 7:47 s, and average P˙ = 8:3 × 10−11 s/s. As in the previous case, it leads to the pulsar age tp ∼ 1500 years, much smaller that the age of SNR, estimated by 104 years. These values of P and P˙ correspond to B = 8 × 1014 Gs. P˙ is not constant, uniform set of observations by RXTE gave much smaller and less definite value P˙ = 2:8(1:4) × 10−11 s/s, the value in brackets gives 1s error. The peak luminosity in the burst rec ∼ 41 reaches Lp 10 ergs/s in the region 25-60 keV, the X-ray luminosity in 2-10 keV band is 35 Lx ≈ 2 × 10 ergs/s is also much higher than the rate of the loss of rotational energy (for average 33 P˙) E˙rot ≈ 10 ergs/s. The burst of December 27, 2004 in SGR 1806-20 was the greatest flare, ∼ 100 times brighter than ever. It was detected by many satellites: Swift, RHESSI, Konus-Wind, Coronas-F, Integral, HEND et al.. Very strong luminosity of this outburst permitted to observe the signal, reflected from the moon by the HELICON instrument on the board of the satellite Coronas-F, what permitted to reconstruct a full light curve of the outburst (Mazets et al. 2005, Frederiks et al. 2007). 2.4 SRG1627-41 Here the giant burst was observed 18 June 1998, in addition to numerous soft recurrent bursts. Its position coincides with the SNR G337.0-0.1, assuming 5.8 kpc distance. Some evidences was obtained for a possible periodicity of 6.7 s, but giant burst did not show any periodic signal (Mazets et al.
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